MIAMI (AP) - Tropical Storm Ophelia strengthened Wednesday off Florida's Atlantic coast, following an erratic path that threatened parts of the state with heavy rain.

Less than two weeks after Hurricane Katrina hit South Florida, tropical storm warnings were posted along a 100-mile stretch from Sebastian Inlet to Flagler Beach. The storm's sustained wind increased to 50 mph from 40 mph earlier in the day, and forecasters said it could reach hurricane strength.

Forecasters warned that the slow-moving Ophelia's path remained uncertain. Some computer models have the storm moving to the east and away from the coast, others have it going west, closer to shore, and some show it heading east and then looping back toward the state.

``Anything is possible,'' said Lixion Avila, a hurricane specialist at the National Hurricane Center in Miami.

Up to 5 inches of rain were expected over the next few days from central Florida to southeastern Georgia, with some isolated areas possibly getting 8 inches.

A tropical storm warning, meaning winds in excess of 39 mph are possible within 24 hours, was posted for about 100 miles of the peninsula's eastern coastline from Sebastian Inlet in southeastern Brevard County to Flagler Beach. A warning for areas south of Sebastian Inlet was discontinued.

At 11 a.m. EDT, Ophelia, the 15th named storm of the season, was centered 85 miles east-northeast of Cape Canaveral. It was moving to the northwest at just 3 mph.

The storm was expected to gradually intensify and could reach hurricane strength, with winds of at least 74 mph, by Thursday, hurricane center meteorologist Eric Blake said.

Florida has been hit by six hurricanes in the past 13 months, including Katrina, which crossed South Florida on Aug. 25, killing 11, before devastating Louisiana and Mississippi last week.

Elsewhere in the Atlantic, Tropical Storm Nate intensified into a hurricane south of Bermuda, and Tropical Storm Maria was upgraded to a hurricane again over the open ocean.

At 11 a.m. EDT, Nate had strengthened into a hurricane with top sustained winds of 80 mph. It was centered about 230 miles south-southwest of Bermuda and was drifting north near 3 mph. It could pass near or just south of Bermuda by Thursday, but was not expected to threaten the United States, forecasters said.

Forecasters said new observations showed that Maria was still a hurricane with 80 mph sustained winds. They had earlier downgraded it to a tropical storm. It was moving northeast near 14 mph toward the colder waters of the north Atlantic.

Nate is the sixth hurricane in a busy Atlantic hurricane season. The season began June 1 and ends Nov. 30. Peak storm activity typically occurs from the end of August through mid-September.